A plow of the type used to remove snow from a roadway includes a blade which rolls the snow upwardly and then moves it transversely across the face of the blade. To accomplish this, the plow includes a moldboard having a curvilinear configuration which terminates in a lower plowing edge or a scraper blade. The scraper blade usually extends in a forward direction and, in effect, digs into the snow and forces the snow onto the curvilinear moldboard. The contour of the moldboard imports a rolling action to the upwardly moving snow and forces the snow transversely across the face of the moldboard and to the side of the plow.
Over the years, many different moldboard configurations of various curvilinear shapes have been experimented with to arrive at a shape which would insure smooth rolling and transverse movement of wet and powdery snow across the moldboard face. A curvilinear configuration, essentially arcuate in shape and extending in only one planar direction has proven an acceptable, widely used geometrical configuration for the moldboard.
A typical snowplow construction is to roll a mild steel carbon plate, typically of about 1/8", into an arcuate shape to form the moldboard. The framework, typically constructed from structural angle members, is then welded to the rear side of the moldboard to support and prevent the moldboard from fracturing when being hit by rock and other debris from the roadway while also providing the structure for the attachments necessary to operate the plow. Typical examples of such construction may be found by reference to U.S. Pat. Nos. 3,432,947 to Peitl and 3,465,456 to Meyer assigned to the current assignee.
From a consideration of plow weight, a steel moldboard is undesirable. It obviously places greater force requirements on the vehicle to which it is attached, and perhaps more importantly requires heavier plow attachments and larger lifting systems than what otherwise may be possible.
From an efficiency consideration, a number of attempts have been made to improve the efficiency of the steel moldboard in plows of the aforesaid type so as to better enhance the rolling motion and transverse movement of the snow across the face of the moldboard. Many of the approaches fundamentally involve a lowering of the coefficient of friction at the surface of the moldboard. For example, wax has long been used by snowplow operators on the moldboard. Moldboards have also been permanently coated with various substances. However, such coatings eventually fail when struck by rocks, stones and other debris from the roadway which impact the moldboard under significant forces.
A number of various materials having extremely low coefficients of friction exist in the art. In particular, ultra high molecular weight polyethylenes have been developed and applied in industrial application where sliding contact is encountered, such as, for example, in wear strips, slide plates, bearings and bushings. Until now, considerations relating to the mechanical properties of such materials have ruled out the suitability of such materials for use as a moldboard in a snowplow application.
More recently, on the basis of weight and cost considerations alone, various types of other plastics have been used as moldboards in snowplows. The plastic is preformed into the desired curvilinear shape and applied flush against the frame were it is drilled and fastened in place in the same manner that the steel moldboard is conventionally applied to the frame. Depending upon the properties of the plastic and its durability, plastic moldboards have met with limited success.
Even more recently, a snowplow and a method of constructing a snowplow which utilizes a high molecular weight, polyethylene material as a moldboard to produce a durable, lightweight and significantly improved snowplow has been disclosed in U.S. Pat. Nos. 4,803,790 and 4,845,866 both to Ciula and assigned to the current assignee and incorporated herein by reference. The plow disclosed in these patents comprises a conventional frame which includes top and bottom longitudinally extending mounting members approximately equal to the length of the plow blade and a plurality of vertically extending, transversely spaced brace members. Each brace member is secured at one end to the top mounting member and at its opposite end to the bottom mounting member and has inwardly curved forward edge surfaces extending between the top and bottom members. A generally rectangular and inwardly curved polyethylene moldboard of high molecular weight is attached by threaded fasteners to the top and bottom mounting members in an inwardly curved, flexed and prestressed manner. The rearward surface of the attached moldboard is spaced away from the forward edge surface of the brace members a fixed distance. This distance is normally sufficient to prevent contact therebetween during operation of the plow while permitting brace contact during excessive debris impact. The moldboard is prestressed when assembled in the frame to a preferred curvilinear shape whereby the rigidity and resiliency of the curvilinear moldboard shape is enhanced to provide good rolling and transverse movement of the snow during normal operation of the plow while the braces in the frame prevent an excessive distortion and/or fracture of the moldboard when debris from the roadway severely impact the moldboard.
In constructing plows formed of inwardly curved polyethylene moldboard of high molecular weight, as disclosed in the U.S. Pat. Nos. 4,803,790 and 4,845,866, the curvature of the moldboard was prestressed or flexed to some degree prior to its attachment to the frame. The assembly required accurately and precisely positioned drilled holes on both the moldboard and frame to receive the threaded fasteners. The threaded fasteners had shanks to provide a near force fit with the holes in the moldboard. The board then was bent into its proper configuration by tightening the threaded fasteners to the frame. This assembly was time consuming and required skilled mechanics in order that the assembled plow had the moldboard properly and securely attached to the frame with the correct curvature. As discussed before, ensuring that the finished plow has a moldboard with the desired curvature is extremely important because the effectiveness with which the moldboard imparts the rolling action to the upwardly moving snow and forces it transversely across the face of the moldboard to the side of the plow is a function of the curvature. Accordingly, in the past, plow manufacture required special assembly jigs, skilled workers and careful attention. Snow plows are typically used in hostile environments which include cold temperatures, moisture, salt, and severe impacts against fixed protrusions such as curbs and from rocks and debris from the roadway. Therefore, when the moldboard occasionally fractured or was otherwise damaged, the frame had to be taken to a skilled dealer for repair. The holes for the fasteners provided high stress points where the moldboard could break or tear during high impact or load conditions. Also, the holes collected moisture, salt and dirt which eventually caused the fasteners to deteriorate and become subject to breakage from a severe impact.